JPH08330882A - Surface acoustic wave element substrate and its manufacture - Google Patents

Abstract

PURPOSE: To obtain an acoustic surface wave element substrate and its manufacture capable of conveniently adjusting a frequency. CONSTITUTION: On a substrate 1 for processing a device, an acoustic surface wave element pattern 15 including at least a piezoelectric body layer 14 arranged on this substrate 1 and an electrode layer 13 arranged so as to contact with the piezoelectric body layer 14 is formed. On both of the side of the forming face 1a of the acoustic surface wave element pattern 15 and the opposite side 1b of the substrate 1 for processing a device, a distortion layer 2 reducing the camber of the substrate 1 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device,
More specifically, on the surface opposite to the surface acoustic wave device device pattern forming (processing) surface of the device processing substrate,
The present invention relates to a surface acoustic wave element substrate having a "strained layer" for controlling the "warp amount" of the substrate, and a method for manufacturing the surface acoustic wave element substrate.

[0002]

2. Description of the Related Art A surface acoustic wave element (hereinafter referred to as "SAW element") which is an element utilizing surface acoustic waves (hereinafter referred to as "SAW") propagating on a solid surface has the following characteristics.

It is small and lightweight.

Excellent in vibration resistance and impact resistance.

Since there are few variations in products, the reliability is high.

Since no adjustment of the circuit can be achieved, the mounting can be easily automated and simplified.

In addition to the characteristics common to the electromechanical functional parts described above, the SAW element further has various characteristics such as excellent temperature stability, long life, and excellent phase characteristics. It can be widely and suitably used as a resonator, a delay device, a signal processing element, a convolver, a functional element for optoelectronics, and the like.

With the recent increase in multi-channel and high frequency in the field of communication including satellite communication and mobile communication, it can be used in a higher frequency range (eg, GHz band) also in the field of the SAW element described above. The development of various devices is required.

Generally, the operating frequency f of the SAW element is f
= V / λ (V is the SAW propagation velocity, λ is the SAW wavelength)
Is determined. The wavelength λ depends on the shape (period, etc.) of the comb-shaped electrode as described later, and the shape of the comb-shaped electrode is microfabricated using photolithography technology.
n) Depends on technology limitations. Therefore, SAW
In order to further increase the frequency of the device, fine processing technology at a finer level is required.

At present, for the purpose of forming a SAW element or a device pattern thereof (device pattern corresponding to one or more SAW elements), microfabrication basically using a photolithography technique is widely used.

Taking the fabrication of a SAW element having a multi-layered structure of comb-shaped electrodes / piezoelectric layer / diamond as an example, fine processing is usually performed on one surface (mirror-polished) of a wafer made of a piezoelectric material or the like. Surface) on the basis of a photolithography process, chemical vapor deposition (CVD, for example, formation of a diamond thin film on a silicon wafer), physical vapor deposition such as sputtering (PVD method, for comb electrodes, for example). Thin film formation technology (such as the formation of Al thin film) and etching technology (for example, the formation of a comb-shaped electrode pattern from the above Al thin film) are combined, and these technologies are repeatedly used as necessary to obtain a desired SAW device device
This is done by forming various films (for example, films having different SAW propagation velocities, films having a positive or negative temperature coefficient, etc.), conductive films (for example, comb-shaped electrodes, wiring), etc., which should form a pattern.

In general, when patterns such as the above-mentioned insulating film and metal film that form a device are laminated or formed on a wafer, the insulating film and the metal film have internal stress after formation, and / or Alternatively, these give stress to the surface or inside of the wafer, and there is a tendency that the wafer itself "warps" after the element formation process or after the element formation based on the imbalance between the stress and the stress derived from other wafer portions. .
The extent of such "warpage" is generally determined by the material of the wafer,
It is said that it depends on the size, the element forming process, and the like.

[0013]

When an SAW element is to be formed on the above-mentioned wafer, for example, when the "warp" of this wafer is large or the degree of "warp" is unknown, the manufacture of the element is performed. In the process, the shape of the comb-shaped electrode formed on the wafer (or the piezoelectric layer / wafer or the laminated body having the piezoelectric layer / diamond layer / wafer structure) varies due to the “warp”, and the above-mentioned f = There arises a problem that the center frequency f determined from the relationship of V / λ deviates from a predetermined design value. Furthermore, when the "warp amount" of the wafer being processed is larger, it may be difficult to form the comb-shaped electrode at the submicron level by photolithography depending on the resolution or depth of focus of the photoresist. obtain.

In general, when the ratio bandwidth (Δf / f; f is the center frequency; the frequencies at which the signal intensity is reduced by 3 dB from the center frequency f is f ₁ and f ₂ respectively), Δf
= | F ₂ −f ₁ |) is 0.3% or less, it is desirable that the variation of the center frequency f is as small as possible. For example, in a narrowband filter using quartz,
The variation of the center frequency f of the final product is within 50 ppm (Appl. Phys. Lett., 39 (1), 40.
(1981)).

However, in a SAW filter having a multi-layer structure in which a piezoelectric material such as zinc oxide or aluminum nitride is arranged on a substrate made of Pyrex glass, silicon, sapphire, diamond or the like, there is a difference in phase velocity between layers. Therefore, the phase velocity of the multilayer structure tends to change depending on the film thickness of the piezoelectric body. Therefore, the variation in the manufacturing lot of the SAW resonator using the multi-layered material is generally larger than that of the SAW resonator using the single material such as quartz crystal. The variation of the SAW resonator in the 5 GHz band has been a variation of about several MHz to several tens of MHz (0.05 to several%) in the past.

Therefore, conventionally, in order to obtain a SAW element to be used as a frequency filter for a narrow band, for example, after the manufacturing process of a desired SAW element is completed,
Post-fabrication adjustmen
t) had to.

As a typical example of such fine adjustment method, in a 500 MHz band SAW element using quartz, dry etching using plasma based on (CF ₄ + O ₂ ) gas is performed after the element is formed. , SAW frequency is known to be finely adjusted (Appl. Phys. Le
tt, 39 (1), p. 40 (July 1, 1981)). The "deviation" of the center frequency in the manufacturing process of the SAW element using crystal is usually about 300 ppm, but such a frequency adjustment method can change the frequency of about 500 ppm at the maximum. It is said that the degree of "deviation" can be controlled within 50 ppm. This frequency adjustment method by plasma etching has been introduced into the SAW element manufacturing process, and actually contributes to the improvement of the yield of the element.

However, with this plasma etching method, it is difficult to finely adjust the "deviation" exceeding 500 ppm. Therefore, for example, a high frequency SAW element of 1.0 GHz or more (usually SiO
₂ / ZnO / diamond; or a multilayer structure of ZnO / sapphire, etc.)
Fine adjustment of the center frequency using only the etching method is difficult. Furthermore, in this plasma etching method, the plasma may damage the piezoelectric body, and when the etching rate is reduced, the formation of a polymer film containing fluorocarbon does not occur. Uniform etching tends to occur easily.

As a method for improving the difficulty of adjusting the etching rate of the plasma etching method, heavy ion (X
e ⁺ ) Impact trimming (frequency trimming)
A precise fine adjustment method of the frequency of the SAW element using the sine wave has been proposed (IEEE Transactions on Ultrasonics, Ferr
oelectrics and Frequency Control, Vol.41, No.
5, 694 (Sep. 1994)). However, in this method, it is necessary to mount the manufactured SAW elements one by one on the holder in the vacuum chamber and to subject the elements to heavy ion bombardment while monitoring the frequency response of the elements. It becomes a little complicated.

An object of the present invention is to provide a SAW element substrate and a method of manufacturing the SAW element substrate, which solves the above problems in the prior art.

Another object of the present invention is to provide a SAW element substrate and a method of manufacturing the same, in which the frequency of a SAW element or a SAW resonator having a multilayer structure can be effectively adjusted.

Still another object of the present invention is to adjust the "warp" of the base material constituting the SAW element to obtain SA.
An object of the present invention is to provide a SAW element substrate whose W center frequency can be adjusted and a manufacturing method thereof.

Still another object of the present invention is to provide a SAW element substrate capable of simple frequency adjustment and a method of manufacturing the same.

[0024]

As a result of earnest research, the present inventor has found that S
In a device processing substrate (wafer, etc.) on which a device pattern of an AW element has already been formed, a "strained layer" for controlling the "warp amount" of the substrate is provided on the surface opposite to the SAW element pattern forming surface. Positive introduction,
It has been found that not only is it extremely effective in reducing the "warpage" of the substrate, but it is also extremely effective as a means for adjusting the frequency of the SAW element.

The surface acoustic wave device substrate of the present invention is based on the above-mentioned findings, and more specifically, it is on a device processing substrate; a piezoelectric layer disposed on the substrate and in contact with the piezoelectric layer. A device pattern of a surface acoustic wave device including at least an electrode layer arranged as described above,
In addition, a strained layer that reduces the “warpage amount” of the substrate is formed on the surface of the device processing substrate opposite to the surface acoustic wave device device pattern forming surface.

According to the present invention, further, on the device pattern forming surface side of the device processing substrate; the piezoelectric layer disposed on the substrate, and the electrode disposed so as to contact the piezoelectric layer. After forming a device pattern of a surface acoustic wave device including at least a layer, reduce the "warp amount" of the substrate on the device processing substrate surface side opposite to the surface acoustic wave device device pattern forming surface. There is provided a method for manufacturing a surface acoustic wave device substrate, which comprises forming a strained layer.

[0027]

On the other hand, in the SAW element substrate of the present invention, a "strain layer" having a function of controlling the "warp amount" of the substrate is provided on the surface of the SAW element opposite to the device pattern forming surface. By actively introducing SA
Fine adjustment of the W center frequency is extremely easy.

Hereinafter, the present invention will be described in detail with reference to the drawings as necessary.

(SAW Element) Referring to FIG. 1 which is a schematic cross-sectional view showing one embodiment of the SAW element of the present invention, device formation of a device processing substrate (for example, a silicon wafer) 1 containing a semiconductor material in at least a part thereof. A SAW element 15 including a diamond layer 12, a comb-shaped electrode 13 arranged on the diamond layer 12, and a piezoelectric layer 14 arranged on the comb-shaped electrode 13 is arranged on the working surface 1a side. Has been done. The SAW element substrate 16 of the present invention is used for such a SAW.
It comprises the element 15 and the substrate 1 described above. In the present invention, a "strained layer" 2 for controlling the center frequency of the substrate 1 is formed on the surface 1b of the device processing substrate 1 opposite to the SAW element formation surface 1a.

The SAW element substrate of the embodiment shown in FIG.
As shown in FIG. 2, the SAW element pattern 15 is formed on the device pattern forming surface 1a side of the material substrate 1 (FIG. 2 (a)) (FIG. 2 (b)), and the device pattern forming surface is formed. The "strained layer" 2 is positively introduced by further performing a predetermined grinding process as will be described later on the back surface 1b side opposite to the side 1a (FIG. 2 (c)).

In the AW element substrate having the above structure, the desired S formed on the device forming surface 1a side is formed.
The “strained layer” in which the stress due to the formation of the AW element pattern (FIG. 2B) (usually the stress due to the diamond layer 12 occupies most) is positively introduced into the back surface 1b.
Compensated by the stress based on 2, the SAW device substrate 16
The stress as a whole is eliminated or reduced.

In the SAW element substrate 16 of the present invention,
The formation of the “strained layer” 2 is particularly effective because at least part of the substrate is in the form of a “laminated substrate”. That is, since the propagation velocity of SAW is generally dispersible with respect to the thickness of each layer, even if the method of finely adjusting the center frequency using a conventional method such as dry etching is directly applied to the “laminate substrate”, It is difficult to achieve the purpose of fine adjustment completely. On the other hand, in the present invention, since the "warpage" of the entire substrate is increased or decreased by introducing the strained layer on the surface on the opposite side where the SAW element pattern is formed, the effect of the center frequency is increased. Control becomes possible.

(Device Processing Substrate) In the present invention, as a material forming the device processing substrate, a material having a SAW propagation velocity different from that of a piezoelectric body described later and a material having a different temperature coefficient are preferably used. Such a substrate material may have a function of holding the piezoelectric body, and / or may be used in combination with another material having a function of holding the piezoelectric body, if necessary.

The above "materials having different SAW propagation velocities" are
It is preferable that the material has a high propagation velocity. More specifically, a high frequency is applied to the input side electrode of the SAW element to excite the SAW, and V = fλ (where f is the center frequency and λ is S
SAW propagation velocity V obtained from the relationship of (AW wavelength)
(M / min), V ≧ 8,000 m / min (further, V ≧ 10,000 m / min) is preferable. The high frequency is 1.0 GHz or higher (further 1.5
It is particularly effective when the frequency is at least GHz. SAW
Since the element can be used in the 0th, 1st, and 2nd modes, the degree of freedom in design is increased when a material having a high propagation speed is used.

Specific examples of the material constituting such a substrate include, for example, heat resistant glass (for example, trade name: Pyrex, manufactured by Corning Glass Works, USA), silicon,
Examples include sapphire and diamond. Further, as the "other material" for supporting these substrate materials, silicon, glass or the like may be used if necessary.

The size of the device processing substrate or wafer made of the above materials is not particularly limited, but from the viewpoint of easy mounting in a fine processing apparatus, for example, the diameter is 2 inches to 8 inches.
A substrate having a size of about inch can be preferably used.

The thickness of the substrate is not particularly limited, but from the viewpoint of easiness of surface mounting and balance of mechanical strength / material cost of the substrate itself, for example, 50 μm to 1000 μm.
A substrate having a thickness of (1 mm) can be preferably used.

(SAW Element) In the present invention, the structure or configuration of the SAW element 15 to be formed on the device processing substrate 1 is the piezoelectric layer 14 disposed on the substrate 1.
And the electrode layer 13 arranged so as to be in contact with the piezoelectric layer 14 are not particularly limited. From the viewpoint of easily obtaining a large SAW propagation velocity (that is, a high operating frequency), between the device processing substrate 1 and the electrode layer 13,
Alternatively, the diamond layer 12 is preferably arranged between the device processing substrate 1 and the piezoelectric layer 14.

(Diamond) In the present invention, as the diamond layer 12 constituting the above SAW element 15, any of single crystal diamond, polycrystalline diamond, and / or epitaxially grown diamond can be used. From the viewpoint of easy formation of the SAW element 15 and easy control of “warpage” of the diamond / substrate (or holding) material structure, the diamond layer 12 has a thickness of about 10 to 50 μm, more preferably 10 to 20 μm.
It is preferably about μm.

In the present invention, the method for growing the diamond (thin) film is not particularly limited. More specifically, for example, as the growth method, a CVD (chemical vapor deposition) method,
Known methods such as a microwave plasma CVD method, a PVD (physical vapor deposition) method, a sputtering method, an ion plating method, a plasma jet method, a flame method and a hot filament method can be used.

(Piezoelectric layer) In the present invention, as the piezoelectric layer 14 constituting the SAW element, a known piezoelectric such as ZnO, AlN, quartz, LiNbO ₃ , LiTaO ₃ can be used without particular limitation. Is.

The thickness of the piezoelectric layer 14 can be appropriately selected according to the type of the piezoelectric body and / or the desired characteristics of the surface acoustic wave device (center frequency, specific bandwidth, temperature characteristics, etc.). it can.

The method of forming the film of the piezoelectric material is not particularly limited. More specifically, for example, as the film forming method, CVD
(Chemical vapor deposition) method, microwave plasma CVD method,
Known methods such as PVD (Physical Vapor Deposition) method, sputtering method, and ion plating method can be used without particular limitation. From the viewpoint of uniformity, mass productivity or piezoelectric characteristics, the sputtering method (especially RF magnetron
The sputtering method) is preferably used.

(Aspect of SAW Element) FIGS. 3 to 6 are partial schematic sectional views showing an example of the layer structure of the SAW element 15 in the present invention.

With reference to FIG. 3, in this embodiment, the SAW element 15 arranged on the silicon substrate 1 is arranged on the diamond layer 12 arranged on the silicon substrate 1, and on the diamond layer 12. The electrode layer 13 and the piezoelectric layer 14 disposed on the electrode layer 13.

On the other hand, in the SAW element of the embodiment shown in FIG. 4, except that the electrode layer 13 is arranged on the piezoelectric layer 14 (not between the diamond layer 12 and the piezoelectric layer 14). This is the same as the third aspect.

FIGS. 5 and 6 show, in addition to the above configuration,
The structure which has arrange | positioned the electrode for short circuits (electrode arrange | positioned as needed) mentioned later is shown. That is, in the embodiment of FIG. 5, the short-circuit electrode 17 is arranged on the surface of the piezoelectric layer 14 (the upper surface of the piezoelectric layer 14) opposite to the surface of the piezoelectric layer 14 on which the electrode layer 13 is arranged. Has been done.

On the other hand, in the embodiment shown in FIG. 6, the short-circuit electrode 17 is arranged between the diamond layer 12 and the piezoelectric layer 14 so as to face the electrode layer 13 with the piezoelectric layer 14 interposed therebetween. There is.

(Electrode Layer) As the shape or structure of the electrode layer 13 constituting the SAW element in the present invention, known ones can be used without particular limitation. Further, the material forming the electrode layer is not particularly limited as long as it is a conductive material. From the viewpoint of conversion to bulk waves, Al (aluminum) can be used particularly preferably.

The thickness of the electrode layer is not particularly limited as long as it functions as an electrode of the SAW element, but it is 100 to 3
It is preferably about 000 angstroms (more preferably about 100 to 500 angstroms).

As the structure of the electrode layer, a so-called "comb electrode" (interdigital transducer, abbreviated as "IDT") can be preferably used.

The planar shape of the comb-shaped electrode is not particularly limited as long as it exhibits the function as the electrode, but a so-called single electrode as shown in FIG. 7 is a so-called single electrode, and a schematic plan view is as shown in FIG. A double electrode or the like can be preferably used.

In the present invention, in addition to the above-mentioned electrode structure, a known electrode structure (for example, the electrode structure described in JP-A-7-58581) can be used without particular limitation.

(Short-Circuiting Electrode) In the SAW element of the present invention, the short-circuiting electrode 17 provided as needed is an electrode having a function of changing the SAW characteristic of the element by making the electric field equipotential. . This short-circuiting electrode 17 is
Usually, the surface of the piezoelectric layer 14 opposite to the surface of the piezoelectric layer 14 on which the electrode layer 13 is arranged (that is, the surface facing the electrode layer 13 with the piezoelectric layer 14 interposed therebetween; in the embodiment of FIG. 5) ,
It is preferably arranged on the upper surface of the piezoelectric layer 14.

The short-circuit electrode is a metal (thin) film (for example, A
1, Au, Al—Cu, etc.). Since the short-circuit electrode 17 has a function different from that of the comb-shaped electrode described above, the material forming the short-circuit electrode is
It does not necessarily have to be the same as the material of the comb electrodes.

The thickness of the short-circuiting electrode 17 is not particularly limited as long as it exhibits the function as the electrode, but it is 100 to 30.
It is preferably about 00 angstroms (more preferably about 100 to 500 angstroms).

It is preferable that this short-circuiting electrode has, for example, a planar shape of a "solid electrode" having the same occupied area as the above comb-shaped electrode.

(Device Pattern of SAW Element) In the SAW element substrate of the present invention, the device pattern of the SAW element may correspond to one SAW element chip or a plurality of SAW element chips. May correspond to.

The above "strained layer" (in the "strained layer",
Usually, the crystal lattice is disturbed and at least partially becomes amorphous) can be confirmed by optical microscope observation or electron microscope observation. "Strained layer"
The thickness of the semiconductor material substrate 1 to the SAW element 15 depends on the type and thickness (for example, the diamond layer 12).
Thickness), but usually 5 μm to 30 μm
It is preferably about the same.

The roughness of the back surface 1b of the SAW element substrate is JIS
It is possible to quantitatively evaluate by R _max , _Ra, etc. defined in B0601-1970. The degree of roughness of the back surface 1b or the thickness of the "strained layer" 2 and SA
It is also possible to control the “warp amount” δ by utilizing the relationship with the “warp” δ to be introduced into the W element substrate 16.

(Measurement of Warp Amount) In the present invention, the method of measuring the “warp amount” δ of the substrate is not particularly limited, and a mechanical contact method, an optical method (for example, Newton ring method) or the like may be used. It is possible.

In terms of accuracy and reproducibility, "warpage amount"
δ is preferably measured by a mechanical contact method. In this mechanical contact method, a commercially available “warp meter” (for example, “Swarf meter” manufactured by Tokyo Seimitsu Co., Ltd., trade name: SURFCO)
M) can be preferably used. This "sled meter" (SUR
When FCOM) is used, the “warp” δ (FIG. 9 or 10) of the wafer after grinding one surface of the wafer can be evaluated as follows (IEEE TRANSACTIONS ON
COMPONENTS, HYBRIDS AND MANUFACTURING TECHNOLOGY,
Vol.13 (No.3), p528-533, SEPTEMBER 1990)).

<Measurement Method of “Warp Amount δ” by Mechanical Contact Method> A substrate on which the “warp amount” is to be measured is set on the reference plane, and the needle of the “warpage meter” is linearly formed from the end of the substrate. Scan the (probe) and measure the vertical displacement of the needle. The maximum value of the vertical displacement thus obtained is referred to as “warpage amount” δ.

The amount of warpage δ measured as described above can be expressed by the following equation (1).

Δ = {σ · r² ・ 3 (1-υ) ・ d_f/ E_s} ((1 / d_s ²) = K ・ (1 / d _s ²) ... (1) In the above formula (1), δ is the “warp” of the wafer, and σ is the stress.
Where r is the wafer radius and E_sIs Young's modulus and υ is Poisson
Ratio, d_fIs the thickness of the strained layer (work-affected layer), d_sIs a wafer
The final thickness of each is shown. The above K is the surface of the earth.
A factor called the ground surface factor
And is used as a measure of wafer "warpage".

By using the above equation (1), it becomes easy to introduce a predetermined warpage amount δ into a predetermined wafer (diameter and thickness) by the above-mentioned grinding process.

The warpage amount δ is determined by the optical interference type (oblique incidence) flat nester utilizing the Newton ring method (for example, manufactured by NIDEK CORPORATION, trade name: high precision digital flat nester T-90A, light source: He). -Ne
Laser, 6328 angstrom, 5 mW) can be used for the measurement by the following method.

<Measurement Method of “Warp Amount δ” by Optical Method> It occurs due to the phase shift based on the optical path difference between the reflected light from the reference surface and the reflected light from the substrate surface whose “warp amount” is to be measured. The number of interference fringes (m) to be counted is δ = (m · λ) /
2 cosy (m: number of interference fringes, λ: laser wavelength, y:
Δ is obtained from the relationship of the solid angle between the reference plane and the substrate plane.

(Method for forming strained layer) In the present invention, S
The method for forming the “strained layer” is not particularly limited as long as the predetermined “strained layer” 2 can be introduced on the back surface 1b side of the AW element substrate 16. From the viewpoint of simplicity, it is preferable to use a grinding method as a method for introducing the “strained layer” 2. Specific examples of this grinding method include a known lapping method on the back surface of the wafer, grinding processing and the like.

From the viewpoint of accurately and uniformly introducing the "strained layer" on only one side, the grinding process is preferably used in the present invention. The back grinding method using a grinding tool (for example, a resin bond diamond wheel) described in JP-A-63-144966 can be particularly preferably used.

(Grinding Tool) A diamond grinding tool (grinding stone) that can be suitably used in the strained layer formation of the present invention is a tool having a structure in which diamond abrasive grains and a filler are fixed with a binder.

The above diamond abrasive grains are components that substantially contribute to grinding, and their size (grain size) is # 2000.
.About. # 4000 is preferable (# 3000 corresponds to a particle size having an average diameter of about 3 .mu.m. For details of the definition of such particle size, JISR6001-1956 can be referred to). The concentration of the diamond abrasive grains is about 60 to 90 (further 70 to 8).
It is preferably about 0). Here, the "concentration degree" is a ratio of diamond abrasive grains in a diamond grinding tool, and is usually an abrasive grain ratio (total volume of diamond abrasive grains ÷ volume of grinding tool) contained in the volume of the grinding tool. "25% by volume" is expressed as "100".

The above-mentioned "filler" is a component that contributes to "bonding" in the grinding tool but does not substantially contribute to grinding, and is composed of solid particles. As the filler, calcium carbonate, alumina, silicon carbide, copper powder or the like can be used. Ratio of filler in grinding tool (volume of filler ÷
The volume of the grinding tool is about 20 to 60% by volume (further 3
It is preferably about 0 to 50% by volume).

The above-mentioned "binder" is obtained by uniformly distributing the diamond abrasive grains and the filler and binding them to each other,
It is a component that gives the grinding tool a certain shape. As the binder, resins such as phenol resin and polyimide resin can be preferably used. The ratio of the binder in the grinding tool (volume of binder / volume of grinding tool) is preferably about 40 to 80% by volume (further, about 50 to 70% by volume).

In the present invention, the grinding tool preferably has a wheel shape, that is, a ring shape.
It is preferable that such a ring-shaped grinding tool (wheel) is fixed to the circumferential end surface of the grindstone head having a “U” -shaped cross section (the result of the fixing is a “bow” shape). Because it is also called a cup-type wheel).

(Back Grinding Grinding) When “back grinding” using the diamond grinding tool described above is used, introduction of “warp” into the SAW element substrate depends on grinding conditions (grinding speed, diamond constituting the grindstone). It is possible to control with high accuracy by setting (selection of grain size of grains, etc.).

For example, when the SAW element 15 is formed on the silicon wafer 1, according to the study of the present inventor,
As shown in the graph of No. 1, it has been confirmed that there is a linear relationship between the diamond grain size (or the resulting “roughness of the back surface 1b”) and the “warpage” δ of the SAW element. Such a relationship has been confirmed in other SAW device materials, for example, SAW devices made of compound semiconductors such as GaAs. According to the knowledge of the present inventor, FIG.
The relationship of 1 is presumed to be because plastic deformability becomes dominant (brittle deformability becomes weak) by increasing the abrasive grain size (that is, decreasing the grindstone grain size). Therefore,
A desired warpage amount δ can be obtained by adjusting the grain size of the abrasive grains.

Further, according to the study by the present inventors, it has been found that a desired warpage amount δ can be obtained by adjusting the grinding speed.

As described above, the "strained layer" 2 for causing a predetermined "warp" to be introduced into the SAW element substrate 16 by adjusting the parameters of the grinding process (grain size of the abrasive grains, grinding speed, etc.). Is even easier.

(Device Processing Substrate) Referring to FIG. 12, in the present invention, the SAW element pattern 15 is formed on the device processing substrate 1 in consideration of the depth of focus in the photolithography process. After performing FIG. 12 (a)), a “strained layer” 2 is introduced into the back surface 1 b surface of the device processing substrate 1 (FIG. 12 (b)), so that the SAW
The central frequency of the entire element substrate 16 can be adjusted. At this time, the use of the relationship as shown in the graph of FIG. 11 makes it easy to introduce a predetermined “warp amount” δ.

According to a study by the present inventor, for example, SAW
At the time of forming a thin film by a vapor deposition method or the like in the device / pattern formation process of the element, the “warp amount” δ is 5 to 10 μm for a 2 inch wafer and 10 to 20 μ for a 3 inch wafer.
In the case of about m, the back-grinding process is performed on the substrate made of silicon by using diamond abrasive grains of about # 2000, so that the “warpage amount” δ is almost 0 (δ ≦ 5 μm or less). ) Was possible.

(Timing of "Strained Layer" Formation) In the present invention, the "strained layer" 2a may be introduced before the desired SAW element pattern 15 is formed on the substrate 1, and is also desired. The “strained layer” 2 may be introduced after the SAW element pattern 15 is actually formed on the substrate 1. Furthermore, these “introduction of the strained layer 2a before forming the SAW element pattern” and “introduction of the strained layer 2 after forming the SAW element pattern” may be combined as necessary.

(Combination with other frequency adjusting method) According to the above-mentioned introduction of the "strained layer" to the back surface of the SAW element substrate,
Although it is possible to perform a desired coarse adjustment or fine adjustment of the frequency of the SAW element, in the present invention, if necessary, from the viewpoint of ease of frequency fine adjustment or frequency fine adjustment suitable for each SAW element. Frequency adjustment based on the introduction of such a “strained layer” and other frequency adjustment methods (for example, the above-mentioned conventional “frequency adjustment method by plasma etching”,
“Frequency adjustment method by heavy ion bombardment”, etc.) may be combined.

Hereinafter, the present invention will be described more specifically with reference to Examples.

[0085]

EXAMPLE 1 (Formation of SAW element pattern on silicon substrate) Referring to FIG. 13, a silicon wafer having a thickness of 1 mm (diameter 5.0
cm, about 2 inches wafer) 1 on one surface of a microwave plasma CV using hydrogen gas with a methane concentration of 2%
A diamond film 12a having a thickness of 35 μm was grown by the D method (FIG. 13A).

<Diamond film forming conditions> Microwave power: 150 w Reaction gas: CH ₄ : H ₂ = 2: 100 Gas pressure: 40 mTorr Film formation temperature: 800 ° C. The diamond film 12 a thus obtained is electrodeposited diamond. Whetstone (diamond grain size: # 2000)
A diamond / Si substrate was obtained by mechanically polishing the diamond film 12 to a thickness of about 20 μm (FIG. 13).
(B)).

Then, the aluminum (Al) thin film 13a is formed on the diamond / Si substrate by DC sputtering so as to have a film thickness of 400 Å.
Were grown (FIG. 13 (c)).

<Aluminum thin film forming conditions> DC power: 500 w Reaction gas: Argon (Ar) Gas pressure: 70 mTorr Film forming temperature: Room temperature The aluminum thin film 13a thus obtained is subjected to a usual photolithography process to form an electrode. A resist pattern 20 corresponding to a comb-shaped electrode pattern having an interval of 1.5 μm and an electrode width of 500 μm was formed (FIG. 13).
(D)). Using the resist pattern 20 as a mask, the aluminum thin film 13a was etched by a reactive ion etching (RIE) method to form a comb-shaped electrode pattern 13 made of an aluminum thin film (FIG. 13 (e)).

<Aluminum thin film etching conditions> RF power: 300 w Reaction gas: BCl ₃ gas pressure: 50 mTorr Etching temperature: 60 ° C. Next, the comb pattern electrode (13) / diamond (12) obtained by removing the resist pattern 20. / Si substrate (1)
A ZnO polycrystal 14 was formed on the laminated structure by RF magnetron sputtering so as to have a film thickness of 0.3 μm (FIG. 14A).

<Sputtering conditions> RF power: 500 w Reaction gas: Argon: Oxygen = 1: 1 Gas pressure: 100 mTorr Film formation temperature: 250 ° C. ZnO (14) / comb-shaped electrode (13) obtained as described above
/ Diamond (12) / Si substrate (1) layered structure on top of SiO by RF magnetron sputtering
_{The two} films 21 were formed to have a film thickness of 0.5 μm (see FIG. 1).
4 (b)).

<Sputtering conditions> RF power: 500 w Reaction gas: Argon: Oxygen = 1: 1 Gas pressure: 80 mTorr Film formation temperature: 150 ° C. Then, a resist pattern (corresponding to a hole for a bonding pad is formed by a photolithography technique ( (Not shown) is formed, and then the SiO ₂ film 21 and the ZnO film 14 constituting the above laminated structure are selectively etched using hydrofluoric acid (HF) to form bonding pad holes 22 in the laminated structure. Formed (FIG. 14 (c)).

Example 2 (Formation of Backside “Strain Layer” of SAW Element Substrate) A vector network analyzer (VNA Yokogawa Hewlett-Packard (YH) was prepared for the SAW element substrate prepared in Example 1.
P), 8719A)
When the center frequency of the AW element was evaluated, it was 10 MHz higher than the design value of 1.500 GHz.

<Evaluation Method of Center Frequency> Using the above VNA, the transmission characteristic (S ₂₁ ) of the scattering parameter (S parameter) was measured, and the frequency with the smallest loss was taken as the center frequency.

On the other hand, the “warp amount” δ of the wafer of the SAW element substrate manufactured in Example 1 was measured by a mechanical contact method using a commercially available “warp meter” (manufactured by Tokyo Seimitsu Co., Ltd., trade name: SURFCOM). The "warpage amount" δ was +0.
It was 0 μm.

The above SAW element substrate is mounted on a wafer grinding apparatus as shown in the schematic front view (and schematic side view) in FIG. 15, and a resin bond diamond wheel as a grinding tool as shown in the schematic sectional view in FIG. Then, the back surface (the surface 1b of the SAW element substrate 16 opposite to the surface 1a on which the SAW element pattern 15 is formed) was ground. FIG.
In the schematic diagram, each symbol has the following meaning.

31 ... I-axis grindstone head, 32 ... II-axis grindstone head, 33 ... Cutting device, 34 ... Work table device, 3
5 ... Work chuck device, 36 ... Chuck cleaning device, 3
7 ... Work cleaning device, 38 ... I-axis spindle motor, 39 ...
II axis spindle motor, 40 ... I axis cutting motor, 41 ... II
Shaft cutting motor, 42 ... Operation panel.

<Resin Bond Diamond Wheel> Grain size of diamond abrasive grains: # 800 (concentration: 75) Filler: calcium carbonate (ratio of filler: 40% by volume) Binder: phenol resin (ratio of binder: 60) Volume%) Wheel size: Wheel diameter 250mm x Whetstone width 2m
m × grinding stone height 3 mm <Grinding conditions> Wheel peripheral speed: 1500 m / min Cutting speed: 200 μm / m Wafer grinding amount: 200 μm The “warp amount” δ of the SAW element substrate after the above grinding treatment is S
When measured by the mechanical contact method using URFCOM in the same manner as above, it was δ = + 7 μm.

Further, the wafer is cut to prepare an ultrathin section for a transmission electron microscope (TEM), and the ultrathin section (S
When observing the thickness direction of the AW element substrate) by TEM (magnification: 5,000 to 30,000 times), it was found that the thickness of the “strained layer” introduced by the above grinding treatment was about 15 μm. In this TEM observation, the distance from the "interface" of the crystal structure / amorphous structure of the SAW element substrate cross section to the back surface of the substrate was taken as the thickness of the "strained layer" (obtained as the average value of the thicknesses at three locations) ).

Example 3 In the same manner as in Example 2, except that the "warpage amount" δ was changed by adjusting the grinding conditions (grain size and / or grinding speed) of the back surface of the SAW element substrate. Warp amount ”δ (μm)
Then, the correlation between the center frequency of the SAW element and the reduction amount (MHz) was obtained, and the relationship shown in the graph of FIG. 17 was obtained.

At this time, the SAW element substrate obtained in Example 1 (Si thickness: 1 mm, diamond layer thickness: 20 μm,
Diamond is deposited in the direction of compression)
When the “strained layer” 2 was introduced in the direction of the compressive stress (direction canceling the compressive stress based on the diamond layer) and the substrate had a Si thickness of 800 μm, the warpage amount δ = 26 μm,
The center frequency of a SAW element with a design value of 1.5 GHz is 9 MH
z got smaller. That is, at the center frequency (9/150
It was possible to adjust 0) × 100 = 0.6%. Similarly, the deviation of the center frequency of about 0.1 to 0.5% could be corrected by controlling the warpage amount δ = several μm (about 0 to 30 μm).

[0101]

As described above, in the SAW element substrate of the present invention, the "warp amount" of the SAW element substrate, that is, the center frequency is controlled on the surface of the device processing substrate opposite to the surface on which the SAW element pattern is formed. Since the "strained layer" having the function to actively introduce the active layer, it is possible to obtain a desired center frequency. Therefore, according to the present invention, the center frequency can be finely adjusted after the desired SAW element is formed.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one aspect of a SAW element substrate of the present invention.

FIG. 2 is a schematic cross-sectional view showing one embodiment of a method of introducing a “strained layer” into a SAW element substrate that can be used in the present invention.

FIG. 3 is a schematic cross-sectional view showing another aspect of the SAW element substrate of the present invention.

FIG. 4 is a schematic cross-sectional view showing still another aspect of the SAW element substrate of the present invention.

FIG. 5 is a schematic cross-sectional view showing still another aspect of the SAW element substrate of the present invention.

FIG. 6 is a schematic cross-sectional view showing still another aspect of the SAW element substrate of the present invention.

FIG. 7 is a schematic plan view showing one aspect (single electrode) of a configuration of comb-shaped electrodes that can be used in the SAW element substrate of the present invention.

FIG. 8 is a schematic plan view showing another aspect (double electrode) of the configuration of the comb-shaped electrode that can be used in the SAW element substrate of the present invention.

FIG. 9 is a schematic cross-sectional view showing the definition of “warpage amount” δ in the present invention (when δ is positive).

FIG. 10 is a schematic cross-sectional view showing the definition of “warpage amount” δ in the present invention (when δ is negative).

FIG. 11 is a graph showing an example of the relationship between the grain size of abrasive grains and the “warpage amount” δ in the present invention.

FIG. 12 is a view showing formation of a SAW element pattern in the present invention.
It is a schematic cross section which shows one aspect which introduce | transduces a "strained layer" into a device processing substrate later .

FIG. 13 is a schematic cross-sectional view showing a step of one aspect of the SAW element substrate forming method used in the examples.

FIG. 14 is a schematic cross-sectional view showing an aspect (a step after the step of FIG. 13) of the SAW element substrate forming method used in the examples.

FIG. 15 is a schematic view showing one embodiment of a grinding device usable in the present invention.

FIG. 16 is a schematic cross-sectional view showing one embodiment of a grinding tool (resin bond diamond wheel) usable in the present invention.

FIG. 17 is a graph showing an example of the correlation of the amount of warpage δ-the amount of reduction of the SAW center frequency obtained in the example.

[Explanation of symbols]

1 ... Device processing substrate, 1a ... Device forming surface, 1
b ... back surface, 2 ... strained layer, 7 ... reference surface, 12 ... diamond layer, 13 ... electrode layer, 14 ... piezoelectric layer, 15 ... SAW element pattern, 16 ... SAW element substrate, 17 ... shorting electrode, 20 ... Resist pattern, 21 ... SiO ₂ film, 22
… Bonding pad holes.

Front page continuation (72) Inventor Hiroyuki Kitabayashi 1-1 1-1 Konyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Shinichi Shikada 1-1-1 Konyo Kita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works

Claims (9)

[Claims] 1. A device pattern of a surface acoustic wave device, comprising: a device processing substrate; and a piezoelectric layer disposed on the substrate and an electrode layer disposed so as to contact the piezoelectric layer. And a strained layer for reducing the “warpage amount” of the substrate is formed on the surface of the device processing substrate opposite to the surface acoustic wave device device / pattern forming surface. And a surface acoustic wave device substrate. 2. The surface acoustic wave element substrate according to claim 1, further comprising a diamond layer disposed between the device processing substrate and the piezoelectric layer. 3. The surface acoustic wave device device pattern, a diamond layer disposed on the device processing substrate, an electrode layer disposed on the diamond layer, and a piezoelectric layer disposed on the electrode layer. The surface acoustic wave device substrate according to claim 2, comprising a body layer. 4. The surface acoustic wave device device pattern, a diamond layer disposed on the device processing substrate, and a piezoelectric layer disposed on the diamond layer,
The surface acoustic wave device substrate according to claim 2, comprising an electrode layer disposed on the piezoelectric layer. 5. The surface acoustic wave device substrate according to claim 1, wherein the surface acoustic wave device device pattern includes a pattern corresponding to a plurality of surface acoustic wave devices. 6. A surface including at least a device pattern forming surface side of a device processing substrate; a piezoelectric layer disposed on the substrate, and an electrode layer disposed so as to be in contact with the piezoelectric layer. After forming the device pattern of the acoustic wave device, forming a strained layer on the surface of the device processing substrate opposite to the surface acoustic wave device device pattern forming surface to reduce the “warpage amount” of the substrate. A method for manufacturing a surface acoustic wave element substrate, comprising: 7. The method of manufacturing a surface acoustic wave device substrate according to claim 6, wherein the surface acoustic wave device device pattern further includes a diamond layer disposed between the device processing substrate and the piezoelectric layer. 8. The method for manufacturing a surface acoustic wave element substrate according to claim 6, wherein the “strained layer” is formed by a grinding process. 9. The method for manufacturing a surface acoustic wave device substrate according to claim 8, wherein the “strained layer” is formed by a grinding process using a resin bond diamond grinding wheel containing diamond abrasive grains.